The present disclosure relates to a laser diode device and to a method of manufacturing a laser diode device. More specifically, the present disclosure relates to a hexagonal III-nitride laser diode device and to a method of manufacturing the same.
A laser diode is currently utilized in enormous numbers of technical fields. In particular, the laser diode is indispensable necessary optical device in the field of image display units such as a television and a projector. In such applications, a laser diode outputting light of red, green, and blue which are light's three primary colors is necessitated, and improvement of laser characteristics is desired.
In Japanese Unexamined Patent Application Publication No. 2009-176837, in order to effectively suppress higher-order mode light in a nitride-based laser diode device used in a short-wavelength region with a wavelength of about 400 nm, a configuration in which an insulating layer containing fine particles that absorb emitted light is formed on side surfaces of a ridge is disclosed. Red and blue laser diodes have been in practical use. Meanwhile, in recent years, a green (a wavelength from about 500 nm to about 560 nm both inclusive) laser diode has been actively developed (for example, see “The World's First True Green Laser Diodes on Novel Semi-Polar {2 0 2 1} GaN Substrates I,” (hereinafter referred to as NPTL1) by Takashi Kyono et al., SEI Technical Review, Vol. 176, pp. 88-92 (January, 2010) and “The World's First True Green Laser Diodes on Novel Semi-Polar {2 0 2 1} GaN Substrates II,” (hereinafter referred to as NPTL2) by Masahiro Adachi et al., SEI Technical Review, Vol. 176, pp. 93-96 (January, 2010)).
In NPTL1 and NPTL2, a III-nitride laser diode (green laser) in which an n-type cladding layer, a light emitting layer including an active layer configured of InGaN, and a p-type cladding layer are laminated in this order on a semi-polar surface {2, 0, −2, 1} of an n-type GaN substrate is proposed. It is to be noted that, in the present specification, a plane direction of a hexagonal crystal is described as {h, k, l, m} (h, k, l, and m represent plane indices).
In NPTL1 and NPTL2, crystal growth of an epitaxial layer is made on the semi-polar surface of the GaN substrate, and thereby, a green laser with superior crystal quality is achieved while influence of piezo electric field is suppressed. In NPTL2, a configuration in the case where a green laser apparatus has a refractive index waveguide (ridge type) structure is described. In the configuration, laser light is confined by forming an insulating layer with low refractive index on side surfaces of a ridge.